libcurl-impersonate was not being used properly, as the code was
overriding the headers set by it to prevent detection.
- update the libcurl-impersonate to an actively managed lexiforest
fork
- impersonate Chrome 131
- move the defaultHttpHeaders to http.php, where it belongs
- only set defaultHttpHeaders if curl-impersonate is not detected
- make useragent ini setting optional and disabled by default
- add necessary documentation updates
* docs: Do not use constant names when referring to config options
The options are customizable using a config file and no longer hardcoded in index.php since 8ac8e08abf
* Do not use constants for configuration
Since <8ac8e08abf>, they are just set to the configuration object values.
